The present invention relates to improvements to gas burners for cookers, comprising a burner head having an approximately frustoconical peripheral side wall with the small cross section thereof located at the top and including a multiplicity of slots distributed peripherally and forming flame orifices, the said burner head being topped by a cover or cap.
In FIG. 1 of the appended drawings, a conventional gas burner arrangement for a cooker has been shown highly schematically. This gas burner essentially comprises, and only as regards the invention, a burner head 1 having a peripheral side wall 2. This peripheral wall 2 is slightly frustoconical with its small cross section located at the top. The peripheral wall 2 is provided with a multiplicity of slots 3, with an approximately horizontal bottom 8, these being distributed peripherally and forming orifices for flames 4. The burner head 1 is topped by a removable cover or cap 5, which closes off the top of the slots 3 and defines the flame orifices.
As regards the rest of the gas burner, this may be constructed in any appropriate manner; in particular, for extra-flat burners, the burner may, in a manner known per se, include a radial annular venturi defined by the lower face of the cap 5.
In currently known gas burners, the side wall 2 of the burner head is inclined only very slightly to the vertical, this angle of inclination typically not exceeding 1 to 3xc2x0. As a result, the flames 4, which leave their respective orifices 3 approximately perpendicular to this wall 2, have a tendency to move substantially away from the wall of the burner head and come into contact with the bottom 6 of a vessel 7 of suitable dimensions for the burner only in the vicinity of the peripheral edge of the said bottom of the vessel, as may be clearly seen in FIG. 1. Under these conditions, the bottom of the vessel is heated less in its central region: the vessel is not heated substantially homogeneously over its entire surface, while an appreciable fraction of the heat escapes to the side and is lost.
U.S. patent application Ser. No. 10/245,939 filed on Sep. 18, 2002 and assigned to the same Assignee, and not yet published, aimed to provide an improved arrangement which, for a given diameter of the burner, leads to an appreciably increased efficiency of the burner and to a substantially increased heating rate, without furthermore this resulting in any complication of the structure or of the manufacture of the burner.
The improved arrangement provided is shown in FIG. 2, in which the representation of the gas burner 1xe2x80x2 is identical to that given in FIG. 1 apart from the improved arrangements, and the same numerical references have been retained in order to denote the components or parts that are unchanged.
The peripheral side wall 2xe2x80x2 has a more pronounced conicity than in the prior burners and its angle of inclination xcex1 to the vertical is around 10xc2x0 to 20xc2x0, typically about 15xc2x0.
In addition, the bottom 8xe2x80x2 of each slot forming a flame orifice, which extends transversely to the said wall 2, has an angle of inclination xcex2 to the horizontal which is around 20xc2x0 to 30xc2x0, typically about 25xc2x0.
Under these conditions, as may be seen in FIG. 2 (in which the cap 5 remains identical, both in shape and in position, to that which it had in FIG. 1), the flames 4 leave the respective orifices 3 closer to the vertical than in the configuration of FIG. 1 so that they reach the bottom 6 of the vessel in a more central region thereof. This bottom is heated more uniformly and, correspondingly, a smaller fraction of the heat escapes to the side. In total, the heat is transmitted to the vessel and to its contents under appreciably better conditions, and the overall efficiency of the burner is substantially improved.
The implementation of the arrangements of the invention results in a shorter heating time, for example to bring a given volume of liquid to boiling. To be more specific, to bring a 6 litre volume of water, contained in a vessel having a diameter of 203 mm, from a temperature of 22xc2x0 C. to a temperature of 98xc2x0 C., a time of around 21 min is required with a burner designed in accordance with the invention, as opposed to about 25 min with a conventionally designed burner. The arrangements according to the invention therefore allow the heating time to be substantially reduced (by around 16% in the example in question) and therefore result in a corresponding saving in gas consumption.
The arrangement of the burner related to in U.S. patent application Ser. No. 10/245,939 is therefore entirely satisfactory within the context of the use for which it was specifically designed.
However, some users, who need rapid burners for certain preparations, also need slow cooking (simmering) for other preparations. In the latter case, the use of a rapid burner turns out to be unsuitable, even if it is set to the minimum power. Thus, these users, not wishing for the cooker to be equipped with a multiplicity of burners having different characteristics, which have proved to be expensive, have expressed the desire to be able to cook slowly and uniformly over a long period of time with the rapid burner, which must, of course, retain its rapid heating characteristics that are so appreciated.
The invention therefore provides an improved arrangement of the aforementioned rapid burner, suitable for making it capable of gentle and uniform cooking when it is set to minimum power, whereas it retains its rapid heating characteristics and qualities when it is set to high power.
For these purposes, the invention provides a burner for a cooker, comprising a burner head bounded by a substantially frustoconical peripheral side wall having a small cross section at the top and including a multiplicity of slots distributed peripherally and forming flame orifices, the said burner head being topped by a cover or cap, in which burner head the side wall has an angle of inclination to the vertical of about 10xc2x0 to 20xc2x0 and in which burner head the bottom of each slot forming a flame orifice, which extends transversely to the said side wall, has an angle of inclination to the horizontal of about 20xc2x0 to 30xc2x0, which burner, being designed according to the invention, is characterized in that the ratio of the diameter of the cap to the diameter of the side wall at approximately mid-height of the outlet orifices of the slots is between about 1.4 and 1.6, in that the stand-off of the lower face of the cap with respect to the bearing surface of the cap on the top of the burner head is between about 1 and 15 mm, preferably about 10 mm, and in that the angle of inclination to the horizontal of the lower face of the cap is between about 3xc2x0 and 15xc2x0, preferably about 10xc2x0.
Thus, the invention aims to give the cap a specific geometry which, in combination with the main arrangements of U.S. patent application Ser. No. 10/245,939, confers two operating modes on the burner:
when the burner is used at minimum power, the flames, which are small, remain contained beneath the cap without being able to extend beyond the outline of the latter; these flames, which are in contact with the peripheral annular region of the lower face of the cap, heat the cap, which then diffuses the heat via its entire upper face towards the bottom of the vessel located above it: this results in well-distributed and gentle heating, propitious for simmering;
when the burner is used at normal or high power, the flames, well formed, go around the cap and the burner operates under the conditions explained in document U.S. Ser. No. 10/245,939 providing rapid heating.
Now, the arrangements according to the invention, which are particularly beneficial because of the two functions in use that they provide, are also particularly beneficial as they are extremely simple to implement; these arrangements rely on a specific geometry of the burner body and of the cap, and they require no additional piece or component.
According to a simple embodiment of the burner of the invention, the aforementioned stand-off of the underface of the cap results from the fact that the lower face of the cap has a platform projecting vertically downwards from the said annular portion which surrounds it, the said platform constituting the bearing surface for the cap to bear on the top of the burner head.